If this has been run through calibre, it is possible to have two or three overlapping (cascading) styles working at the same time. Don't be discouraged if your first attempt to correct it doesn't work. Do work only on a copy so you can keep the original intact in case your repair attempt causes incidental damage.

Margins can also be set in the .xpgt file (not part of the epub standard, but used by a lot of publishers, it is an Adobe extension to epub). Sigil will put any xpgt file in the Misc folder in the tree view.

Did the book come from InDesign? It tends to add those long decimal portions to picture sizes, which then fail validation.
Not that I've ever achieved export of a page with a picture layout from InDesign that was good for anything other than deletion and a re-make.

Did the book come from InDesign? It tends to add those long decimal portions to picture sizes, which then fail validation.
Not that I've ever achieved export of a page with a picture layout from InDesign that was good for anything other than deletion and a re-make.